Pallbearers carry a small casket into a Mt. Lebanon church, while hundreds of toy trucks continue piling up at the funeral home where Maddox Derkosh was mourned. "Trucks For Maddox" will help a kids' Christmas charity.

Two wreaths hang at the still-closed exhibit, next to some candles, flowers, a stuffed teddy bear, a picture of an angel and the words, "Our thoughts and prayers are with you." All items were placed there by zoo visitors who wanted to express sympathy. (SLIDESHOW: Memorial forms for boy at zoo)

Maddox Derkosh's mother picked him up and put him on top of a railing at the edge of a viewing deck late Sunday morning when he lost his balance and fell, zoo President Dr. Barbara Baker said. There was a safety net below the railing, but it failed to catch and the child dropped more than 10 feet into the enclosure.

"The child was so small that he bounced. He bounced twice and then he bounced into the exhibit," said Baker, who teared up at a news conference Monday afternoon.

The Allegheny County Medical Examiner's Office said the boy died of blood loss from trauma caused by the dogs. Authorities said his mother is 34 and lives in Pleasant Hills. (RELATED: Facebook fundraiser for family)

“Just the best people you'd ever want to meet. As parents, they adored him. He was there everything,” said family friend Tamara Stark. “She was the most awesome mother -- so caring, so loving.”

Stark told Channel 4 Action News reporter Marcie Cipriani she believes the boy's mother lifted him up onto the railing because he "wore glasses and couldn’t see very well."

"Almost immediately after that, he lost his balance, fell down off the railing into the pit, and he was immediately attacked by 11 dogs," Pittsburgh police Lt. Kevin Kraus said. "It was very horrific."

The attack was so violent and quick that by the time a veterinarian and other zoo staffers arrived seconds later, they determined it would have been futile to try a rescue, Baker said.

"Once the child was in the exhibit, there simply wasn't anything anyone could have done, and it was over very quickly," she said.

Zookeepers called off some of the dogs after the boy fell in the exhibit, and seven of them immediately went to a back building. Three more eventually were drawn away from the child, but the last dog was aggressive and police said they had to shoot it.

"As we were passing the tigers, we went up towards, we could hear screaming over the hillside, saying 'stay away, stay away,' " zoo visitor Bart DePasquale said.

"A man came running out with the kids, and I asked him what was going on, and he said, 'I can't tell you, there's too many kids around,' " zoo visitor Mike Gordon said.

Baker said zoo staffers fired blank darts at the dogs instead of actual tranquilizers because they would also be harmful to humans. "We had to be sure we didn't do any harm to the young boy in our efforts to recover him and help him," she said.

The painted dogs are about as big as medium-sized domestic dogs, and weigh 37 to 80 pounds, according to the zoo. They have large, rounded ears and dark brown circles around their eyes and are considered endangered. (SLIDESHOW: Photos of the zoo's painted dogs)

The attack happened in the Painted Dog Bush Camp, which is part of a larger open area where elephants, lions and other animals can be seen. Visitors walk onto a deck that is glassed on the sides and open in front where the railing is located. Kraus said there was nothing to prevent visitors from jumping into the exhibit area.

Baker said the zoo -- which never had a visitor death before -- will also launch an internal investigation. She said the dogs have been quarantined but will not be euthanized.

The zoo will face investigations from Pittsburgh police and the District Attorney's Office, the U.S. Department of Agriculture and the Association of Zoos and Aquariums. "They're going to see if there were any potential violations of the Animal Welfare Act that may have contributed to this incident," said USDA spokesman Dave Sacks.

Steve Feldman, a spokesman for the Association of Zoos and Aquariums, said the zoo successfully completed its five-year review in September, which means it meets or exceeds all safety standards.